1. Field of the Invention
The invention relates to a method for producing panels which are cut out of a large format support board with a core of derived timber product.
2. Discussion of Background Information
EP 1 454 763 A2 discloses a method for finishing a wooden board or a board of derived timber product, especially MDF or HDF board with a top and a bottom, in which first of all a sealing layer of melamine resin is applied to the top of the board, a decoration is imprinted onto the sealing layer and then a protective layer of melamine resin is applied to the decoration. Then the structure of the board is compressed under the action of temperature until the protective layer and the sealing layer bond are connected to one another with the inclusion of the imprinted decoration.
DE 195 32 819 A1 discloses a method for producing a board of derived timber product with an optically configurable surface in which a base dye, sealing, a print base and a decorative print are applied in succession to the board of derived timber product. The print base is built up out of a base tint or base coat of lacquer sealing and a surface lacquer. By means of engraving cylinders, a decorative print is imprinted on the print base for example in two-color printing. Finally, a multilayer acrylate UV lacquer which can be cured by means of UV light can be applied to this print.
DE 197 51 115 A1 discloses a method for coating of a panel in which at least one colored layer is applied to the surface, by means of a printing method, especially by means of screen printing. In this case the surface can be untreated, ground or pretreated, especially lacquered. Finally the applied colored layer can be covered by a coating with varnish.
In the use of direct printing technology, therefore direct imprinting of the individual layers on the support board, as a result compared to conventionally produced panels the thickness of the finished laminate panels is reduced by omitting the paper layers. This leads to problems in assembly line production when the large-format coated boards are then divided to produce the panels. To ensure that individual panels do not drop out due to insufficient thickness from DIN 13329, high quality assurance must be pursued; this on the one hand slows down production, and on the other hand also increases production costs. Ultimately irritation among dealers and/or end consumers occurs since the stack height of directly coated boards deviates visibly from conventionally coated boards.
In known board production, conventionally HDF boards are used as support boards whose surface is ground off by roughly 0.3 mm. On the top and the bottom of the support board a press skin is formed which is also called a press patina or rotting layer. The press skin is formed in the molding of the fiber cake and is produced by a hot surface of the pressure plates or belts of the press. The press skin has a thickness of roughly 0.3 mm. Since the press skin is completely ground off and roughly 0.1 mm of the core material is ground off for reducing the peak to valley height on the surface of the support board before further coating, the boards must be made thicker by a corresponding grinding additive; this adversely affects production costs. In order to manufacture a standard floor laminate which has been produced by means of direct printing technology with a thickness of 6 mm, the support board must have at least a thickness of 6.1 mm.
The press skin must be ground off because the action of heat in its region in hot pressing is so high that the adhesive sets too quickly, by which glue bridges partially break and which make the applied layer sensitive. This breaking of the glue bridges makes finished panels susceptible to raising of the decorative and wearproof layers which have been applied to the support board. This raising is called delamination; it can occur under normal loading and can be of a change in magnitude which is typical of derived timber products as a result of climatic fluctuations.
There is therefore a great demand for wearproof laminate panels which are within the thickness tolerance in the aforementioned standard. Furthermore there is a demand for a resource-saving method for production, in which extra costs from additional method steps and/or due to additional materials are largely avoided.